Could the low dosage of birth control pill cause pregnancy?

This is my first time taking birth control pill. I got to know already that I have to wait approximately 2 weeks to a month before letting my guy cum inside me before they start working. ( Is it true?) I am much concerned that my doctor started me off with a low dosage of pills. What's the risk of getting pregnant by taking a low dosage plus letting him cum inside me? Please help.[/b]